1. Field of the Invention
The present invention relates to a valuable metal recycling method and apparatus for recovering valuable metals from an electrode material of a lithium secondary battery.
2. Description of Related Art
The positive electrode of a lithium secondary battery is formed of a lithium-containing transition metal oxide, more specifically, of a composite material containing lithium cobaltate (LiCoO2) comparatively easily produced by synthesis and carbon. The composite material contains Co and Li, which are valuable rare metals. Therefore it is desired to recover Co and Li from the composite material forming the positive electrode of the lithium secondary battery by a recycling process to use the recovered Co and Li for forming electrodes, etc.
A conventional valuable metal recycling method of recovering valuable materials from the material of the positive electrode by a wet process recovers a cobalt compound and the like by a plurality of oxide processing steps.
A recycling process is disclosed in JP-A 10-158751. This known recycling process includes the steps of roasting used lithium secondary batteries, reducing the roasted materials of used lithium secondary batteries with carbon to produce materials that can be easily converted into metal condensates, such as metallic cobalt particles and metallic nickel particles, crushing the roasted materials into particles, sifting the particles to classify the particles into rich particles rich in valuable metals and lean particles lean in valuable metals, mixing the rich particles having a high valuable metal content and a calcium compound to prepare a mixture, melting the mixture by heating at 1500° C. or above, and removing Al from a molten mixture by adding a calcium compound into the molten mixture to obtain valuable metals, such as Co and Li.
A valuable metal recovering process disclosed in JP-A 10-287864 includes the steps of immersing active materials forming the positive electrodes of lithium secondary batteries in a mineral acid, such as sulfuric acid, or a mixed solution of a mineral acid and hydrogen peroxide to produce an eluate, mixing the eluate in a solvent containing a special metal extractant, such as a bis(1,1,3,3-tetra-methylbutyl)phosphoric acid compound for catalytic extraction fractionation, and mixing an extract solution in a mineral acid for back extraction to recover valuable metals.
Those known oxide processing methods include many processes including an acid dissolution process, a solvent extraction process, a deposition process, an acid treatment and a heat treatment and need a longtime to complete the methods. A burning process for removing carbon needs a large quantity of energy and takes a long time on the order of 2 hr. Moreover, the conventional method is unable to recover lithium efficiently. Furthermore, to process an electrode material containing other valuable rare metals, other processing methods suitable for processing such an electrode material are necessary.